Abstract A large cavity in karst was detected during exploratory horizontal drilling ahead of the face in the Qiyueshan tunnel at DK363+629. Exploratory borings were used to determine the shape of the cavity. An injection test was carried out for the karst cavity with a total injection volume of 1613m3, but the test was unsuccessful. A water discharge test was then conducted for the karst cavity with a water release volume of 3000 m3/h continuously for 144h. The water volume was estimated at 430 thousand cubic meters and the water pressure was around 0.2 MPa. The water pressure rose constantly due to rainfall, which showed that the cavity was connected to the ground surface with a continuous water supply. The water discharge test was stopped to ensure construction safety. Natural draining was adopted after breaking through the parallel adit and the principle of "energy releasing and pressure reduction" was followed. The total volume of discharged water was around 630 thousand cubic meters, and the water pressure was dropped to 0.0 MPa from 0.4 MPa, with a steady rate of water flow around 1000 m3/h. Finally, blasting was employed for the cavity and pipe draining was used without changing the direction of water flow and affecting the whole underground water system.
Abstract：
A large cavity in karst was detected during exploratory horizontal drilling ahead of the face in the Qiyueshan tunnel at DK363+629. Exploratory borings were used to determine the shape of the cavity. An injection test was carried out for the karst cavity with a total injection volume of 1613m3, but the test was unsuccessful. A water discharge test was then conducted for the karst cavity with a water release volume of 3000 m3/h continuously for 144h. The water volume was estimated at 430 thousand cubic meters and the water pressure was around 0.2 MPa. The water pressure rose constantly due to rainfall, which showed that the cavity was connected to the ground surface with a continuous water supply. The water discharge test was stopped to ensure construction safety. Natural draining was adopted after breaking through the parallel adit and the principle of "energy releasing and pressure reduction" was followed. The total volume of discharged water was around 630 thousand cubic meters, and the water pressure was dropped to 0.0 MPa from 0.4 MPa, with a steady rate of water flow around 1000 m3/h. Finally, blasting was employed for the cavity and pipe draining was used without changing the direction of water flow and affecting the whole underground water system.
LUO Wen-Xue
.Techniques for Treating a High-pressure Water-filled Cavity in Qiyueshan Tunnel on Yichang-Wanzhou Railway[J] MODERN TUNNELLING TECHNOLOGY, 2011,V48(4): 116-121
2011, Vol. 48 